| Message ID | 20210119172607.18400-1-vincenzo.frascino@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kasan: Add explicit preconditions to kasan_report() | expand |
On Tue, Jan 19, 2021 at 08:35:49PM +0000, Vincenzo Frascino wrote: > On 1/19/21 6:52 PM, Catalin Marinas wrote: > > On Tue, Jan 19, 2021 at 07:27:43PM +0100, Andrey Konovalov wrote: > >> On Tue, Jan 19, 2021 at 6:26 PM Vincenzo Frascino > >> <vincenzo.frascino@arm.com> wrote: > >>> > >>> With the introduction of KASAN_HW_TAGS, kasan_report() dereferences > >>> the address passed as a parameter. > >>> > >>> Add a comment to make sure that the preconditions to the function are > >>> explicitly clarified. > >>> > >>> Note: An invalid address (e.g. NULL pointer address) passed to the > >>> function when, KASAN_HW_TAGS is enabled, leads to a kernel panic. > >>> > >>> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> > >>> Cc: Alexander Potapenko <glider@google.com> > >>> Cc: Dmitry Vyukov <dvyukov@google.com> > >>> Cc: Leon Romanovsky <leonro@mellanox.com> > >>> Cc: Andrey Konovalov <andreyknvl@google.com> > >>> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> > >>> --- > >>> mm/kasan/report.c | 11 +++++++++++ > >>> 1 file changed, 11 insertions(+) > >>> > >>> diff --git a/mm/kasan/report.c b/mm/kasan/report.c > >>> index c0fb21797550..2485b585004d 100644 > >>> --- a/mm/kasan/report.c > >>> +++ b/mm/kasan/report.c > >>> @@ -403,6 +403,17 @@ static void __kasan_report(unsigned long addr, size_t size, bool is_write, > >>> end_report(&flags); > >>> } > >>> > >>> +/** > >>> + * kasan_report - report kasan fault details > >>> + * @addr: valid address of the allocation where the tag fault was detected > >>> + * @size: size of the allocation where the tag fault was detected > >>> + * @is_write: the instruction that caused the fault was a read or write? > >>> + * @ip: pointer to the instruction that cause the fault > >>> + * > >>> + * Note: When CONFIG_KASAN_HW_TAGS is enabled kasan_report() dereferences > >>> + * the address to access the tags, hence it must be valid at this point in > >>> + * order to not cause a kernel panic. > >>> + */ > >> > >> It doesn't dereference the address, it just checks the tags, right? > >> > >> Ideally, kasan_report() should survive that with HW_TAGS like with the > >> other modes. The reason it doesn't is probably because of a blank > >> addr_has_metadata() definition for HW_TAGS in mm/kasan/kasan.h. I > >> guess we should somehow check that the memory comes from page_alloc or > >> kmalloc. Or otherwise make sure that it has tags. Maybe there's an arm > >> instruction to check whether the memory has tags? > > > > There isn't an architected way to probe whether a memory location has a > > VA->PA mapping. The tags are addressed by PA but you can't reach them if > > you get a page fault on the VA. So we either document the kasan_report() > > preconditions or, as you suggest, update addr_has_metadata() for the > > HW_TAGS case. Something like: > > > > return is_vmalloc_addr(virt) || virt_addr_valid(virt)); > > > > This seems not working on arm64 because according to virt_addr_valid 0 is a > valid virtual address, in fact: > > __is_lm_address(0) == true && pfn_valid(virt_to_pfn(0)) == true. Ah, so __is_lm_address(0) is true. Maybe we should improve this since virt_to_pfn(0) doesn't make much sense. > An option could be to make an exception for virtual address 0 in > addr_has_metadata() something like: > > static inline bool addr_has_metadata(const void *addr) > { > if ((u64)addr == 0) > return false; > > return (is_vmalloc_addr(addr) || virt_addr_valid(addr)); > } As Andrey replied, passing a non-zero small value would still be incorrectly detected as valid.
On 1/20/21 4:04 PM, Catalin Marinas wrote: > On Tue, Jan 19, 2021 at 08:35:49PM +0000, Vincenzo Frascino wrote: >> On 1/19/21 6:52 PM, Catalin Marinas wrote: >>> On Tue, Jan 19, 2021 at 07:27:43PM +0100, Andrey Konovalov wrote: >>>> On Tue, Jan 19, 2021 at 6:26 PM Vincenzo Frascino >>>> <vincenzo.frascino@arm.com> wrote: >>>>> >>>>> With the introduction of KASAN_HW_TAGS, kasan_report() dereferences >>>>> the address passed as a parameter. >>>>> >>>>> Add a comment to make sure that the preconditions to the function are >>>>> explicitly clarified. >>>>> >>>>> Note: An invalid address (e.g. NULL pointer address) passed to the >>>>> function when, KASAN_HW_TAGS is enabled, leads to a kernel panic. >>>>> >>>>> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> >>>>> Cc: Alexander Potapenko <glider@google.com> >>>>> Cc: Dmitry Vyukov <dvyukov@google.com> >>>>> Cc: Leon Romanovsky <leonro@mellanox.com> >>>>> Cc: Andrey Konovalov <andreyknvl@google.com> >>>>> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> >>>>> --- >>>>> mm/kasan/report.c | 11 +++++++++++ >>>>> 1 file changed, 11 insertions(+) >>>>> >>>>> diff --git a/mm/kasan/report.c b/mm/kasan/report.c >>>>> index c0fb21797550..2485b585004d 100644 >>>>> --- a/mm/kasan/report.c >>>>> +++ b/mm/kasan/report.c >>>>> @@ -403,6 +403,17 @@ static void __kasan_report(unsigned long addr, size_t size, bool is_write, >>>>> end_report(&flags); >>>>> } >>>>> >>>>> +/** >>>>> + * kasan_report - report kasan fault details >>>>> + * @addr: valid address of the allocation where the tag fault was detected >>>>> + * @size: size of the allocation where the tag fault was detected >>>>> + * @is_write: the instruction that caused the fault was a read or write? >>>>> + * @ip: pointer to the instruction that cause the fault >>>>> + * >>>>> + * Note: When CONFIG_KASAN_HW_TAGS is enabled kasan_report() dereferences >>>>> + * the address to access the tags, hence it must be valid at this point in >>>>> + * order to not cause a kernel panic. >>>>> + */ >>>> >>>> It doesn't dereference the address, it just checks the tags, right? >>>> >>>> Ideally, kasan_report() should survive that with HW_TAGS like with the >>>> other modes. The reason it doesn't is probably because of a blank >>>> addr_has_metadata() definition for HW_TAGS in mm/kasan/kasan.h. I >>>> guess we should somehow check that the memory comes from page_alloc or >>>> kmalloc. Or otherwise make sure that it has tags. Maybe there's an arm >>>> instruction to check whether the memory has tags? >>> >>> There isn't an architected way to probe whether a memory location has a >>> VA->PA mapping. The tags are addressed by PA but you can't reach them if >>> you get a page fault on the VA. So we either document the kasan_report() >>> preconditions or, as you suggest, update addr_has_metadata() for the >>> HW_TAGS case. Something like: >>> >>> return is_vmalloc_addr(virt) || virt_addr_valid(virt)); >>> >> >> This seems not working on arm64 because according to virt_addr_valid 0 is a >> valid virtual address, in fact: >> >> __is_lm_address(0) == true && pfn_valid(virt_to_pfn(0)) == true. > > Ah, so __is_lm_address(0) is true. Maybe we should improve this since > virt_to_pfn(0) doesn't make much sense. > How do you propose to improve it? >> An option could be to make an exception for virtual address 0 in >> addr_has_metadata() something like: >> >> static inline bool addr_has_metadata(const void *addr) >> { >> if ((u64)addr == 0) >> return false; >> >> return (is_vmalloc_addr(addr) || virt_addr_valid(addr)); >> } > > As Andrey replied, passing a non-zero small value would still be > incorrectly detected as valid. > I would like to remove the check completely and have virt_addr_valid(addr) to return the right thing if possible. I admit, yesterday evening I did not thing it through completely before posting this code that had the sole purpose to open the discussion. I agree in principle on what Andrey said as well (addr < PAGE_SIZE).
On Wed, Jan 20, 2021 at 04:16:02PM +0000, Vincenzo Frascino wrote: > On 1/20/21 4:04 PM, Catalin Marinas wrote: > > On Tue, Jan 19, 2021 at 08:35:49PM +0000, Vincenzo Frascino wrote: > >> On 1/19/21 6:52 PM, Catalin Marinas wrote: > >>> On Tue, Jan 19, 2021 at 07:27:43PM +0100, Andrey Konovalov wrote: > >>>> On Tue, Jan 19, 2021 at 6:26 PM Vincenzo Frascino > >>>> <vincenzo.frascino@arm.com> wrote: > >>>>> > >>>>> With the introduction of KASAN_HW_TAGS, kasan_report() dereferences > >>>>> the address passed as a parameter. > >>>>> > >>>>> Add a comment to make sure that the preconditions to the function are > >>>>> explicitly clarified. > >>>>> > >>>>> Note: An invalid address (e.g. NULL pointer address) passed to the > >>>>> function when, KASAN_HW_TAGS is enabled, leads to a kernel panic. > >>>>> > >>>>> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> > >>>>> Cc: Alexander Potapenko <glider@google.com> > >>>>> Cc: Dmitry Vyukov <dvyukov@google.com> > >>>>> Cc: Leon Romanovsky <leonro@mellanox.com> > >>>>> Cc: Andrey Konovalov <andreyknvl@google.com> > >>>>> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> > >>>>> --- > >>>>> mm/kasan/report.c | 11 +++++++++++ > >>>>> 1 file changed, 11 insertions(+) > >>>>> > >>>>> diff --git a/mm/kasan/report.c b/mm/kasan/report.c > >>>>> index c0fb21797550..2485b585004d 100644 > >>>>> --- a/mm/kasan/report.c > >>>>> +++ b/mm/kasan/report.c > >>>>> @@ -403,6 +403,17 @@ static void __kasan_report(unsigned long addr, size_t size, bool is_write, > >>>>> end_report(&flags); > >>>>> } > >>>>> > >>>>> +/** > >>>>> + * kasan_report - report kasan fault details > >>>>> + * @addr: valid address of the allocation where the tag fault was detected > >>>>> + * @size: size of the allocation where the tag fault was detected > >>>>> + * @is_write: the instruction that caused the fault was a read or write? > >>>>> + * @ip: pointer to the instruction that cause the fault > >>>>> + * > >>>>> + * Note: When CONFIG_KASAN_HW_TAGS is enabled kasan_report() dereferences > >>>>> + * the address to access the tags, hence it must be valid at this point in > >>>>> + * order to not cause a kernel panic. > >>>>> + */ > >>>> > >>>> It doesn't dereference the address, it just checks the tags, right? > >>>> > >>>> Ideally, kasan_report() should survive that with HW_TAGS like with the > >>>> other modes. The reason it doesn't is probably because of a blank > >>>> addr_has_metadata() definition for HW_TAGS in mm/kasan/kasan.h. I > >>>> guess we should somehow check that the memory comes from page_alloc or > >>>> kmalloc. Or otherwise make sure that it has tags. Maybe there's an arm > >>>> instruction to check whether the memory has tags? > >>> > >>> There isn't an architected way to probe whether a memory location has a > >>> VA->PA mapping. The tags are addressed by PA but you can't reach them if > >>> you get a page fault on the VA. So we either document the kasan_report() > >>> preconditions or, as you suggest, update addr_has_metadata() for the > >>> HW_TAGS case. Something like: > >>> > >>> return is_vmalloc_addr(virt) || virt_addr_valid(virt)); > >>> > >> > >> This seems not working on arm64 because according to virt_addr_valid 0 is a > >> valid virtual address, in fact: > >> > >> __is_lm_address(0) == true && pfn_valid(virt_to_pfn(0)) == true. > > > > Ah, so __is_lm_address(0) is true. Maybe we should improve this since > > virt_to_pfn(0) doesn't make much sense. > > How do you propose to improve it? Check that it's actually a kernel address starting at PAGE_OFFSET. The current __is_lm_address() check just masks out the top 12 bits but if they were 0, this still yields a true result. Maybe extending the current definition as: #define __is_lm_address(addr) ((u64)(addr) >= PAGE_OFFSET && \ ((u64)(addr) & ~PAGE_OFFSET) < (PAGE_END - PAGE_OFFSET)) Which basically means: #define __is_lm_address(addr) ((u64)(addr) >= PAGE_OFFSET && \ (u64)(addr) < PAGE_END) I think we could write the above as: #define __is_lm_address(addr) (((u64)(addr) ^ PAGE_OFFSET) < (PAGE_END - PAGE_OFFSET)) This way we catch any 0 bits in the top 12 (or 16 with a 48-bit VA configuration).
Hi Andrey, On 1/19/21 8:56 PM, Andrey Konovalov wrote: >> return (is_vmalloc_addr(addr) || virt_addr_valid(addr)); > Do we need is_vmalloc_addr()? As we don't yet have vmalloc support for HW_TAGS. It is not necessary but it does not hurt, since we are going to add vmalloc anyway at some point, I would keep it here.
On Thu, Jan 21, 2021 at 12:30 PM Vincenzo Frascino <vincenzo.frascino@arm.com> wrote: > > Hi Andrey, > > On 1/19/21 8:56 PM, Andrey Konovalov wrote: > >> return (is_vmalloc_addr(addr) || virt_addr_valid(addr)); > > Do we need is_vmalloc_addr()? As we don't yet have vmalloc support for HW_TAGS. > > It is not necessary but it does not hurt, since we are going to add vmalloc > anyway at some point, I would keep it here. OK, let's keep it.
diff --git a/mm/kasan/report.c b/mm/kasan/report.c index c0fb21797550..2485b585004d 100644 --- a/mm/kasan/report.c +++ b/mm/kasan/report.c @@ -403,6 +403,17 @@ static void __kasan_report(unsigned long addr, size_t size, bool is_write, end_report(&flags); } +/** + * kasan_report - report kasan fault details + * @addr: valid address of the allocation where the tag fault was detected + * @size: size of the allocation where the tag fault was detected + * @is_write: the instruction that caused the fault was a read or write? + * @ip: pointer to the instruction that cause the fault + * + * Note: When CONFIG_KASAN_HW_TAGS is enabled kasan_report() dereferences + * the address to access the tags, hence it must be valid at this point in + * order to not cause a kernel panic. + */ bool kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip) {
With the introduction of KASAN_HW_TAGS, kasan_report() dereferences the address passed as a parameter. Add a comment to make sure that the preconditions to the function are explicitly clarified. Note: An invalid address (e.g. NULL pointer address) passed to the function when, KASAN_HW_TAGS is enabled, leads to a kernel panic. Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Alexander Potapenko <glider@google.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Andrey Konovalov <andreyknvl@google.com> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> --- mm/kasan/report.c | 11 +++++++++++ 1 file changed, 11 insertions(+)